Sun

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 The Sun is a star located about 26,000 light years from the center of the Milky Way.

Looking at the cover image, one wonders how close could a living creature get before it quite literally fries? Credit: web “sciencefocus.com” author: Robert Matthews

Until 1925 it was believed that the entire universe was in a galaxy we call the “Milky Way“.  We now know that there are more than 100 billion galaxies.

Milky Way
Actually astronomers are mapping the arms of the Milky Way. Credit: web “sciencemag.org/news

It is estimated that in our galaxy, the Milky Way, there are more than 100,000 million stars.  One of these stars, a medium-sized and middle-aged one, is our Sun.

It is convenient to have this information to get a more accurate idea of ​​how small the human being is.

How is the sun really

This NASA image shows in great detail what the surface of this immense mass that gives us life on Earth is like.

Sun
Image from May 29, 2020, from NASA’s Solar Dynamics Observatory   Credits: NASA/Solar Dynamics Observatory/Joy Ng.

The Sun is spherical in shape, like all stars.

Its diameter is 1,392,000 km. More than 100 times greater than that of Earth.

Because of its slow rotational movement (one spin takes about 28 Earth days), it has a slight flattening at the poles.

Remember that you should NEVER, NEVER, NEVER look directly at the Sun, and even less through a telescope.

The sun’s rays are not only made up of visible light, but also X-rays, gamma rays, ultraviolet light and infrared light, which, without any doubt, would seriously damage the retina of your eyes.

The Sun is made up of 81% hydrogen, 18% helium; the remaining 1% are other items.

It is estimated that the core of the Sun (384,000 km in diameter) is 49% hydrogen; 49% helium and that the remaining 2% (carbon and nitrogen).

The Sun formed about 4.5 billion years ago from clouds of gas and dust that contained debris from previous generations of stars.

From it arose the Earth, the planets, the asteroids and all the celestial bodies that orbit around them, forming the Solar System.

Much of the information we now have on the structure of the Sun is due to the painstaking and sacrificial work of some intelligent women.

Two of them are well known: Assumpció Català and Margaret Burbidge.

Galileo observed spots on the surface of the sun

With the invention of the telescope, in 1610 Galileo and some other scientists observed some spots on the solar surface.

This contradicted the theory of the total perfection of the Sun and it was decided to attribute the spots to bodies that orbited around the Sun, but were not part of it.

Galileo
Galileo didn’t invent the telescope, but he made significant improvements to it.  Credit: web “biography.com”

In the image, Galileo Galilei is depicted observing the night sky.

But he also observed the Sun and the blindness that Galileo suffered in his later years is believed to have been due in large part to long periods of observation of the Sun, although he did so in the late afternoon and when there was already some fog.

This of the spots on the Sun, openly contradicted the teachings of Aristotle and the universal beliefs that the Sun was one of the perfect and immutable celestial bodies.

All Western sages admitted that the Sun is a luminous, bright sphere, without any spot, that revolved around the Earth.

Even the superiors of a Jesuit astronomer warned him not to go overboard with his speculations that there were spots on the Sun. The Jesuit decided to keep quiet.

Galileo insisted that the spots were part of the solar surface and that they moved along with the rest of the surface.

Galileo was based on he had observed that the Sun made a complete rotation around its axis, in little more than 27 days, and that the spots they advanced at the same time as the rest of the solar surface.

Astronomers after Galileo continued to observe these blobs or so-called blobs, and over time they all came to the idea that they were part of the solar surface.

The Sun moves around the center of the Milky Way

The Sun moves around the center of the Milky Way, and it takes about 225 million years to go through a complete orbit.

Milky Way
Artistic composition of the Milky Way.Crédito: NASA

Solar Energy

Most of the energy sources used by man and by living beings on Earth come directly or indirectly from the Sun.

All the energy that human beings need can be found in the Sun.

Solar energy
The term solar panel is used colloquially for a photo-voltaic module.  Credit: web “en.wikipedia.org”

Fossil fuels preserve solar energy captured millions of years ago through photosynthesis.

Core of the Sun

In the early 1930s, German and American physicists discovered that a group of reactions involving carbon and nitrogen as catalysts constitute a cycle, which is repeated over and over again, as long as the hydrogen lasts.

This group of reactions is known as the “Bethe or carbon cycle” and consists of four protons fusing into a helium nucleus.

In these fusion reactions, 600 tons of hydrogen are transformed into 596 tons of helium every second.

The other 4 tons have been transformed into energy according to Einstein’s equation (E = mc2). The enormous energy produced maintains the solar core at temperatures of approximately 15 million degrees Kelvin.

Sun parts
ESA, NASA’s SOHO Reveals Rapidly Rotating Solar Core. Credit: web “nasa.gov”

Another fusion reaction that occurs in the Sun and in stars is the Critchfiel or proton-proton cycle.

Charles Critchfield, was in 1938 a 34-year-old physicist.

He realized that when two protons collide at high speed, one of them loses its positive charge and becomes a neutron that remains attached to the other proton, forming a deuteron (heavy hydrogen nucleus) and giving off a large amount of energy.

This fusion occurs not only in stars that are hotter and more massive than the Sun, but also in stars similar to the Sun.

Until 1953 it was believed that solar energy was produced almost exclusively by the Bethe cycle.

However, it has subsequently been shown that solar heat comes mainly (almost 75%) from the proton-proton cycle.

Sun parts
Various parts and areas of the sun   Credit: Microsoft illustration

When all the hydrogen is used up, the Sun will contract, due to its own gravitational pull.

This contraction will produce excess energy that will expel the outer layers, causing it to cool down and turn into a red giant star.

The solar diameter will become so great that it will exceed, in addition to Mercury and Venus, the Earth. Currently the Earth is about 150 million km from the Sun.

Solar system
Eight planets of the solar system Credit: Wikipedia

However, there are those who believe that the loss of mass that the Sun suffers during these energy production processes causes the Sun-Earth gravitational attraction to decrease, with which it will gradually place itself in an increasingly more orbit.

Radiation zone of the Sun

Surrounding the nucleus is the so-called radiation zone, composed of large amounts of ionized hydrogen and helium.

It is a tremendously dense medium, through which the photons produced by the nuclear reaction try to escape to the outside.

The solar temperature goes from 15 million degrees at the core to 5,000 degrees at the surface.

It is estimated that any photon takes a million years to reach the surface and manifest as visible light.

Convection zone of the Sun

Above the radiant zone, the energy transport is carried out by convection, in a non-homogeneous and turbulent way by the fluid itself. Fluids expand when heated and decrease in density.

Therefore, upward currents of material are formed from the hot zone to the upper zone, and simultaneously downward movements of material occur from the cold outer zones to the inside.

Turbulent convective sections are thus formed, in which patches of hot and light plasma rise up to the photosphere, where the hot plasma gives up its energy in the form of visible light, cooling before descending again to the depths.

This area is almost 200,000 km thick.

Photosphere of the Sun

The photosphere is the area from which most of the Sun’s visible light is emitted.

The photosphere is considered the solar surface and, seen through a telescope, is made up of bright granules that are projected onto a darker background.

Photosphere
Photosphere, visible surface of the Sun, from which is emitted most of the Sun’s light.  Credit: web “britannica.com”

The photosphere is considered to be 100-200 km deep.

It takes a photon on average a million years to pass through the radiant zone, but in a month it travels the 200,000 km of the convective zone, and in just about 500 seconds it reaches from the Sun to Earth.

It’s not that photons travel faster outside, but rather that their movement inside the Sun is hampered by continual changes of direction, collisions, bumps, and turbulence.

The photosphere is a continuously boiling mass in which the convective cells are seen as glowing, moving granules whose half-life is only about nine minutes.

The average diameter of the individual granules is about 900 km and they are particularly noticeable in periods of minimal solar activity.

There are also turbulent movements on a larger scale, the so-called supergranulation, with diameters of about 35,000 km.

Chromosphere of the Sun

The most obvious sign of activity in the photosphere are sunspots, already observed by Galileo with his telescope, using the projection method on a blank surface.

A single spot can measure up to 12,000 km (almost as large as the diameter of the Earth), but a group of spots can reach 120,000 km in length.

Sunpots
In this image, you can see an active region on the sun with dark sunspots. Credit: NASA/SDO/AIA/HMI/Goddard Space Flight Center

The darkness seen in a sunspot is caused solely by a contrast effec.

If we could see one of the dark spots that are the size of the Earth, in isolation and at the same distance as the Sun, it would be 50 times brighter than the full Moon.

The chromosphere is a visually much more transparent layer outside the photosphere.

Its size is approximately 10,000 km and it is impossible to observe it without special filters as it is eclipsed by the greater brightness of the photosphere.

The chromosphere can be observed in a solar eclipse; it has a characteristic reddish hue.

Solar prominences occasionally rise from the photosphere reaching heights of up to 150,000 km in spectacular solar flares.

Solar corona

The solar corona is made up of the thinnest layers of the upper atmosphere.

Its temperature reaches millions of degrees, a figure much higher than that in the photosphere. This thermal inversion is one of the main puzzles in recent solar science.

These extremely high temperatures are misleading data and a consequence of the high speed of the few particles that make up the solar atmosphere.

In reality, these temperatures are only an indicator of the high velocities that coronal material reaches.

The truth is that this layer is too thin to be able to speak of temperature in the usual sense of thermal agitation.

Sun corona
The corona is generally hidden by bright light from the sun’s surface. The corona can be seen during a total solar eclipse. Credit: web “spaceplace.nasa.gov”

The solar corona is made up of the thinnest layers of the upper atmosphere.

The solar corona is only observable from space with suitable instruments or during a solar eclipse from Earth.

Its temperature reaches millions of degrees, a figure much higher than that in the photosphere. This thermal inversion is one of the main puzzles in recent solar science.

These extremely high temperatures are misleading data and a consequence of the high speed of the few particles that make up the solar atmosphere.

In reality, these temperatures are only an indicator of the high velocities that coronal material reaches.

The truth is that this layer is too thin to be able to speak of temperature in the usual sense of thermal agitation.

Solar wind

As a result of its high temperature, a large amount of X-ray energy is emitted from the corona.

Sola wind
Solar wind magnetic field interacts the Earth’s magnetic field Credit: NASA, web “researchgate.net”

The thin material of the corona is continuously expelled by the strong solar radiation giving rise to the solar wind.

Solar storms

Sun sturms
Solar flares could wipe out the power grid for days or even weeks. Credit: NASA/SDO/AIA, web “nbcnews.com”

Every 11 years, the Sun enters a turbulent cycle of maximum solar activity that causes storms that release waves of radiation and solar wind.

A period of maximum solar activity occurred in 2011.

Sun storms
Can we survive a solar storm? Credit: web “sciencefocus.com/Space/”

A powerful solar storm is capable of completely paralyzing the electricity grid in large cities, a situation that could last for weeks, months or even years.

Solar storms can interfere with radio signals, affect air navigation systems, damage telephone signals, and completely disable satellites in their path.

On March 13, 1989, Québec City, Canada, was hit by a strong solar storm. As a result, six million people were affected by a major blackout that lasted 90 seconds.

Montreal’s power grid was paralyzed for more than nine hours. The damage caused by the blackout, along with the losses caused by the lack of power, reached hundreds of millions of dollars.

Control of solar activity

At present, solar activity is constantly monitored by ground-based astronomical observatories and space observatories.

Sun control
NASA Keeps a Close Eye on the Sun’s Irradiance Credit: web “nasa.gov”

Among the objectives of these observations is not only to achieve a better understanding of solar activity but also the prediction of events with high emission of particles potentially dangerous for activities in space and in telecommunications.